1. Field of the Invention
The invention relates to a multilayer plastic pipe based on polyvinylidene fluoride comprising an outer layer (I), an inner layer (II) and a layer (III) disposed between said layers (I) and (II) based on a mixture of polyamide and polyalkyl acrylate.
2. Discussion of the Background
Plastic pipes made from polyamide have previously been employed for a variety of applications. It is known that in order to achieve their objective, the pipes must be, inter alia, inert to the medium flowing in them, and must be resistant to high and low temperatures and mechanical stresses.
Single-layer pipes are not always capable of satisfying the necessary requirements. In the case of transport of, for example, aliphatic or aromatic solvents, fuels or the like, they exhibit considerable disadvantages, such as a poor barrier action to the medium, undesired changes in dimension or inadequate resistance to mechanical stresses.
Attempts to overcome these disadvantages have included the use of multilayer pipes (DE-A 35 10 395; DE-A 37 15 251; DE-A 38 21 723; DE-A 40 01 125 and DE-A 40 01 126). However, practical implementation of these proposals has shown that, although some disadvantages can be overcome, the overall property profile is still unsatisfactory.
French Patent 2 602 515 describes a two-layer pipe comprising an outer layer of nylon 11 and an inner layer of plasticized polyvinylidene fluoride. However, investigations have shown that the barrier action to the flowing medium is unsatisfactory.
In particular, permeation of methanol-containing fuels has only been reduced to an inadequate extent by means of the abovementioned proposals.
Reduction in permeation by using novel intermediate layers is therefore of crucial importance because, in particular, the legally permitted emission values are constantly being reduced.